Wood pulp fiber morphology modifications through thermal drying

ABSTRACT

A method of modifying a two-dimensional, flat fiber morphology of a never-been-dried wood pulp into a three-dimensional twisted fiber morphology without the aid of a chemical cross-linker. The method includes the steps of treating a never-been-dried wood pulp fiber slurry with a drying aid and thermally drying the wood pulp fiber slurry. The method may alternatively, or additionally, include the steps of spray drying a wood pulp fiber slurry and/or a slurry of a hydrophilic material, and flash drying the spray dried wood pulp fiber slurry and/or slurry of hydrophilic material.

RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 10/025,213, filed Dec. 18, 2001. The disclosure of the priorapplication is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention is directed to methods of modifying wood pulpfiber morphology to produce three-dimensional coiled fibers without theaid of a chemical cross-linker.

Wood pulp is commonly used to make paper as well as absorbent articles.When wood pulp fibers are flat, or roughly two-dimensional, the fiberslack absorbency and softness compared to wood pulp fibers that arecoiled, or three-dimensional.

Never-been-dried wood pulp has many fine pores within the cell walls ina multi-lamellar fashion. The pores are commonly referred to asintra-fiber capillaries, in contrast to inter-fiber capillaries that areformed between individual fibers. The intra-fiber capillaries of anever-been-dried pulp are highly vulnerable to outside forces such asthe surface tension of water, electrolytes, mechanical and thermaltreatments to name a few. In particular, intra-fiber capillaries areeasily collapsed during conventional thermal drying, such as during drumdrying.

When the intra-fiber capillaries of a never-been-dried pulp collapseduring drying, the width, or diameter, of individual fibers shrinks. Asa result, the morphology of once-dried wood pulp tends to be flat andribbon-like, and the intra-fiber capillaries practically disappear.

If a never-been-dried fiber does not shrink uniformly during drying, itsfiber morphology will be quite different from the conventionalribbon-like fiber morphology. Such fibers that shrink non-uniformly arelikely to be coiled or twisted. The degree of coils or twists perindividual fiber depends on the number of intra-fiber capillaries withinthe wood pulp and the degree of non-uniform shrinkage of fiber diametersalong their fiber axes, i.e., perpendicular to the fiber diameterdirection.

Flash drying is a well-known thermal drying method used to dry variousmaterials, such as wood pulps, gypsum, and native starch. In flashdrying, a wet material is exposed to a very hot drying air (or gas)environment without any constraints at a very short time, for example, afew seconds. These drying conditions of a flash dryer for wood pulpfibers can cause fibers to be in a non-equilibrium state during dryingso as to make the fibers shrink non-uniformly. This results in fibershaving coiled structures. In addition, such a short drying time providesvery little opportunity for the pores within the fibers to collapse,thereby resulting in enhanced absorptive properties for the fibers.

Unfortunately, however, flash drying conditions also have a tendency tocause fibers to be entangled, thus forming a so-called fish eye (orfiber bundles, nodules), not just causing the fibers to be twisted.Consequently, a typical commercial flash dryer has been designed tominimize the fiber entanglements and twists.

Curly, twisted cellulose fibers can be produced by permanentlyinterlocking the intra-fiber capillaries with a chemical cross-linkerprior to flash drying. The use of a chemical cross-linker is unfavorablefor a number of reasons. In particular, the use of a chemicalcross-linker involves safety concerns since chemical cross-linkers aregenerally hazardous and harmful. Therefore, the use of a chemicalcross-linker requires a thorough washing of un-reacted chemicalcross-linker for safety. Also, the use of a chemical cross-linker islikely to cause interlocking between fibers that would be difficult tobe fiberized into individual fibers for a product application. Potentialdamage to the fibers may occur during the defibration stage due tointerlocking of the fibers. It can be difficult to form an absorbentproduct due to such interlocking of fibers. Furthermore, the use of achemical cross-linker is not very economical due to the complexity ofhandling such a chemical cross-linker.

More importantly, with respect to the present invention, suchpermanently interlocking intra-fiber capillary structures tend to makethe fibers stiffened and destroy all the useful capillaries as fluidchannels.

In order to obtain a very short drying time during a thermal dryingprocess such as flash drying, it is necessary to fluff pulp so that thelargest possible pulp surface is exposed to the hot drying air. Inparticular, the wet pulp must be thoroughly fluffed as individual fibersprior to flash drying, otherwise dried fibers come out as fiber bundles,or entanglements. Once fibers are entangled during flash drying, thefibers are very difficult to be disentangled into individual fibers forsubsequent uses. Thus, the fluffing operation is the key to a successfulflash drying system.

To use a feed of wood pulp and/or various other hydrophilic materialsfor flash drying, the water in the wet pulp should be removedsubstantially. This water removal is conventionally achieved bymechanical means such as a filter press or centrifugation. At such ahigh consistency level, it is very difficult to fluff the pulp intoindividual fibers. To alleviate this problem, a mechanical device suchas a disintegrator is commonly employed after the mechanical de-wateringstep in the flash drying system.

It is therefore an object of the present invention to provide a methodof modifying wood pulp fiber morphology to produce three-dimensionalcoiled fibers without the aid of a chemical cross-linker.

It is another object of the present invention to maintain the originalintra-capillary structure of wood pulp fiber during a rapid thermaldrying process to utilize the structure of the wood pulp fiber as fluidchannels.

It is yet another object of the present invention to use a drying aid,such as a surfactant, to maximize the extent of twisting and to helpmaintain the porous structures of wood pulp fibers during a rapidthermal drying process.

It is still another object of the present invention to provide analternative method of fluffing wet pulp into individual fibers asopposed to using conventional mechanical devices.

SUMMARY OF THE INVENTION

The present invention is generally directed to methods of modifying thetwo-dimensional, flat, ribbon-like fiber morphology of a typicalnever-been-dried wood pulp into a three-dimensional, coiled, helical,spiral, twisted fiber morphology. The invention is applicable to woodpulp fibers as well as a slurry of hydrophilic materials such asmicrocrystalline cellulose, microfibrillated cellulose, orsuperabsorbent material, or a combination of any of these.

In one embodiment of the invention, the fiber morphology of a typicalnever-been-dried wood pulp is modified without the aid of a chemicalcross-linker. Instead, such modification is achieved using thermaldrying technologies with drying aids. More particularly, the degree ofnon-uniformity of fiber shrinkage inducing the formation of fiber coilsis increased when a never-been-dried pulp is thermally dried under anextremely high drying temperature for a very short drying time withdrying aids for removing water from the intra-fiber capillaries. A flashdryer can be used to thermally dry the fibers.

The never-been-dried pulp can be treated with a drying aid, and watercan then be removed from the pulp up to a consistency level at which theintra-fiber capillaries remain unchanged. As a drying aid, any material,such as a surfactant, that speeds up removing water from the intra-fibercapillaries can be used.

In another embodiment, a never-been-dried wood pulp can be subjected toa refining treatment to create more intra-fiber capillaries. After thefines are removed, the wood pulp fibers can be treated with a drying aidprior to thermal drying, such as flash drying.

In yet another embodiment of the invention, spray drying is carried outto prepare a feed of wood pulp or other hydrophilic materials forsubsequent flash drying. It may be very difficult to fluff the wood pulpinto individual fibers when the consistency of the wet pulp is about 30%to about 50%, and such consistency is needed to use the feed in a flashdryer. Instead of using a mechanical device, such as a disintegrator,after the mechanical de-watering step in the flash drying system, analternative method of fluffing the pulp is carried out by drying thepulp slurry, having a consistency ranging from less than 0.1% to about3% by weight, in a spray dryer until the pulp reaches a desirableconsistency for subsequent flash drying. Preparing a pulp feed from adilute pulp slurry by spray drying in this manner eliminates themechanical de-watering step and the fluffing system entirely in theflash drying system.

Preparing a pulp of a desirable consistency (around 15% to about 60% byweight) for subsequent flash drying by spray drying should be much moreeffective in fluffing the pulp into individual fibers than by usingconventional mechanical means. The modified pulp fibers are particularlysuitable for making paper and absorbent products.

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fiber twist.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present invention is generally directed to methods of modifying woodpulp fiber morphology to produce three-dimensional coiled fibers.Instead of using a chemical cross-linker, the fibers can be modifiedusing thermal drying technologies, such as flash drying, with dryingaids. The invention also teaches the use of spray drying in lieu of amechanical de-watering step and a fluffing system in a flash dryingsystem.

Before describing representative embodiments of the invention, it isuseful to define a number of terms for purposes of this application.These definitions are provided to assist the reader of this document.

“Drying aid” refers to any material, such as a surfactant, that speedsup the removal of water from intra-fiber capillaries of a fiber.

“Fiber” or “fibrous” refers to a particulate material wherein the lengthto diameter ratio of such particulate material is greater than about 10.Conversely, a “nonfiber” or “nonfibrous” material is meant to refer to aparticulate material wherein the length to diameter ratio of suchparticulate material is about 10 or less.

“Fiber twist” refers to the fiber morphology of a coiled or twistedfiber, as shown in FIG. 1.

“Flash dryer” and “flash drying” refer to a thermal drying method inwhich wet material is exposed to a hot air (or gas) stream at a veryshort residence time as a means of drying the wet material.

“Fluff” and “fluffing” refer to a state or process in which fibrousagglomerates are separated into individual fibers.

“Hydrophilic” describes fibers or the surfaces of fibers which arewetted by the aqueous liquids in contact with the fibers. The degree ofwetting of the materials can, in turn, be described in terms of thecontact angles and the surface tensions of the liquids and materialsinvolved. Equipment and techniques suitable for measuring thewettability of particular fiber materials or blends of fiber materialscan be provided by a Cahn SFA-222 Surface Force Analyzer System, or asubstantially equivalent system. When measured with this system, fibershaving contact angles less than 90° are designated “wettable” orhydrophilic, while fibers having contact angles greater than 90° aredesignated “nonwettable” or hydrophobic.

“Never-been-dried” is a term used to describe fibers that have neverbeen exposed to a drying process, such as thermal drying or forced airdrying.

“Refining treatment” refers to treatment of fibers that causes fracturesand fibrillations which aid in imparting strength to resultingapplications in which the fibers are used.

“Spray dryer” and “spray drying” refer to a method and apparatus fortransforming feed from a fluid state to a dried particulate form byspraying the feed into a hot drying medium, typically a hot gas.

“Thermal drying” refers to a process of drying fibers or other materialin which heat is used to accelerate the drying.

“Twist count” refers to the number of twist nodes present along alongitudinal axis of a fiber over a certain length of the fiber. Twistcount is used to measure the degree to which a fiber is rotated aboutits longitudinal axis. The term “twist node” refers to a substantiallyaxial rotation of 180 degrees about the longitudinal axis of the fiber,wherein a portion of the fiber (i.e., the “node”) appears dark relativeto the rest of the fiber when viewed under a microscope with transmittedlight because the transmitted light passes through an additional fiberwall due to the above-mentioned rotation.

“Water Retention Value (WRV)” refers to the volume of theintra-capillaries within the fibers. It is conventionally determinedaccording to the following method: A sample of 0.700+0.100 oven-dry gramof the sample is put into a specimen container, with a lid. The totalvolume in the container is brought up to 100 ml with purified (distilledor deionized) water. Gentle dispersion techniques are applied to thespecimen until the nit or clumps of fibers are not present. Thedispersed fibers are collected by removing excess water with a filtersystem under vacuum. The fibers are then placed into a centrifuge tubewith a screen and the fibers are centrifuged at a relative centrifugeforce of 900 gravities for 30 minutes. When the centrifuge is completed,the tube cap is removed with a dissecting needle to retrieve the fibersfrom the filter paper in the tube. After taring a weighing dish, thefibers are weighed and the wet weight of the fibers is recorded. Theweighing dish is then placed with the fibers in a 105±2 degrees Celsiusoven for a minimum of 12 hours. The dried fibers are then weighed. Thewater retention value (WRV) is calculated using the following equation:WRV=(W−D)/D, wherein W is the wet weight of the fibers, and D is the dryweight of the fibers. The WRV is in units of grams of water per gram ofdry fiber.

One version of a method possessing features of the present inventionincludes modifying a two-dimensional, flat, ribbon-like fiber morphologyof a never-been-dried wood pulp into a three-dimensional coiled,helical, spiral, twisted fiber morphology without the use of a chemicalcross-linker. Instead, a method of the present invention is carried outusing a drying aid and thermal drying technologies.

The methods of the invention can be used to modify virtually any type ofwood pulp, including but not limited to chemical pulps such as sulfiteand sulfate (sometimes called Kraft) pulps, as well as mechanical pulpssuch as ground wood, thermomechanical pulp and chemithermomechanicalpulp. Pulps derived from both deciduous and coniferous trees can beused. Although the invention is directed to the modification of woodpulp fiber morphology, the invention may also be used to modify themorphology of other hydrophilic materials in a slurry. For example, theinvention can be used on such hydrophilic materials as microcrystallinecellulose, microfibrillated cellulose, superabsorbent material, or acombination of any of these materials, or any of these materials incombination with wood pulp fibers.

The principle behind the present invention is that a never-been-driedfiber that does not shrink uniformly during drying will have a fibermorphology quite different from conventional ribbon-like fibermorphology. Non-uniformly dried fibers are likely to be coiled ortwisted, and the degree of coils or twists per individual fiber dependson the amount of the intra-fiber capillaries of wood pulp and the degreeof non-uniform shrinkage of fiber diameters along their fiber axes,i.e., perpendicular to the fiber diameter direction. The degree ofnon-uniformity of the fiber shrinkage inducing the fiber coils isexpected to increase when a never-been-dried pulp is thermally driedunder an extremely high drying temperature and a very short drying timewith drying aids for removing water from the intra-fiber capillaries.

Suitable thermal drying technologies include flash drying and spraying.More particularly, the thermal drying is carried out at a temperature ofat least 180 degrees Celsius, or at least 200 degrees Celsius, or atleast 220 degrees Celsius, suitably at least 250 degrees Celsius, or atleast 300 degrees Celsius. The thermal drying is carried out for betweenabout 0.1 and about 20 seconds, suitably between about 0.1 and about 10seconds, or between about 0.1 and about 2 seconds.

Flash drying is a well-known thermal drying method used to dry variousmaterials, such as wood pulps, gypsum, and native starch, for example.To produce coiled or twisted fibers from a wet pulp, the pulp should bethoroughly fluffed as individual fibers prior to flash drying. Forexample, the fluffing device described in U.S. Pat. No. 3,987,968,herein incorporated by reference, subjects moist cellulosic pulp fibersto a combination of mechanical impact, mechanical agitation and airagitation to create a substantially knot-free fluff. To use a feed to aflash dryer, the water in the wet pulp should be removed substantially,up to about 30% to about 50% consistency by weight. This water removalis conventionally achieved by mechanical means, such as a filter pressor centrifugation. At such a high consistency level, it is verydifficult to fluff the pulp into individual fibers. To alleviate thisproblem, a mechanical device such as a disintegrator is commonly usedafter the mechanical de-watering step in the flash drying system.

As a drying aid, any material that speeds up the removal of water fromthe intra-fiber capillaries can be used. Suitable drying aids includesurfactants, such as an anionic surfactant, a cationic surfactant, or acombination of an anionic surfactant, a cationic surfactant and anon-ionic surfactant. An example of a commercially available drying aidis a cationic surfactant available from Goldschmidt Chemical of Dublin,Ohio, under the trade name ADOGEN 442. Another example of a commerciallyavailable drying aid is an anionic surfactant available from CytecIndustry of Morristown, N.J., under the trade name AEROSOL OT-75. Thesurfactant can be added to fiber individually or in the sequence ofcationic surfactant first and then anionic surfactant. In one embodimentof the invention, a never-been-dried wood pulp is treated with a dryingaid, and water is removed from a pulp up to a consistency level at whichthe intra-fiber capillaries remain unchanged.

Optionally, the never-been-dried wood pulp can be subjected to arefining treatment to create more intra-fiber capillaries. After thefines are removed, the wood pulp can then be treated with a drying aidand then may be thermally dried.

To avoid any fluffing problems, the fluffing step, as well as themechanical de-watering step, can be eliminated by instead drying thepulp slurry in a spray dryer until the pulp reaches a desirableconsistency for subsequent thermal drying. Spray drying is anotherwell-known thermal drying method, typically used for producing powderedproducts from solutions. Spray drying is generally carried out byplacing the slurry or pulp into a large chamber through which a hot gasis blown, thereby removing most or all of the volatiles and enabling therecovery of the dried fibers.

Spray drying is an effective way of preparing a feed of wood pulp,and/or other hydrophilic materials, for subsequent flash drying. Spraydrying is useful for preparing a feed of wood pulp, and/or otherhydrophilic materials, after being chemically or mechanically modifiedfor subsequent flash drying. A pulp slurry having a consistency as lowas less than 0.1% to about 10% by weight can be dried in a spray dryerprior to thermal drying. Preparing a pulp of a desirable consistency,namely between about 15% and about 80% by weight, suitably between about15% and about 50% by weight, for subsequent flash drying by spray dryingis much more effective in fluffing the pulp into individual fibers thanusing conventional mechanical means.

Once the fibers have been modified according to the method of theinvention, at least 80%, or at least 85%, or at least 90% of the treatedfibers include fiber twists. An illustration of a twisted fiber 20 isshown in FIG. 1. As can be seen in FIG. 1, intra-fiber capillarieswithin the fiber twists remain intact. More particularly, fibersmodified in accordance with the invention can have an average dry fibertwist count of at least about 1.5 twist nodes per millimeter, or atleast about 2.0 twist nodes per millimeter, or at least about 2.5 twistnodes per millimeter, and an average wet fiber twist count of at leastabout 1.5 twist nodes per millimeter, or at least about 2.0 twist nodesper millimeter. Twist count can be determined using the test methoddescribed below. Futhermore, the modified fibers can maintain at least70% of the dry fiber twist count over time after rewetting the dryfiber.

Water retention value (WRV) of the fibers may decrease slightly as aresult of carrying out the method of the invention, however, the WRVshould be at least 0.8 grams of water per gram of dry fiber (g/g), or atleast 1.0 g/g, or at least 1.1 g/g, or between 0.8 g/g and 1.5 g/g.Several examples illustrating the formation of fiber twists and changesin WRV are provided below.

Because of their remarkable absorbency and because they are very bulky,soft, and compressible, the wood pulp or other hydrophilic fibersmodified according to the present invention are particularly suitablefor use in paper, tissue, towels, absorbent materials and absorbentarticles, including diapers, training pants, swim wear, feminine hygieneproducts, incontinence products, other personal care or health caregarments, including medical garments, or the like. It should beunderstood that the present invention is applicable to fibers used inother structures, composites, or products incorporating absorbent fibersthat can be modified according to the methods of the present invention.

EXAMPLES Example 1

Flash Drying a Rewet Southern Softwood Kraft Fiber

A dry southern softwood kraft fiber (CF 416, available from WeyerhauserCo. of Federal Way, Wash., U.S.A.) was made into a slurry and wasdewatered to 15% consistency. Then the fiber was fed into a lab scale2-inch by 2-inch Flash Dryer with 5 to 10 pounds per hour waterevaporation capacity (available from Barr-Rosin Inc. of Bolsbriand,Quebec, Canada). The operations were conducted as follows:

-   1st stage: Inlet temperature 620 degrees Fahrenheit-    Outlet temperature 350 degrees Fahrenheit-    Outlet consistency 32.6%-   2nd stage: Inlet temperature 460 degrees Fahrenheit-    Outlet temperature 250 degrees Fahrenheit-    Outlet consistency 88%-   3rd stage: Inlet temperature 460 degrees Fahrenheit-    Outlet temperature 250 degrees Fahrenheit-    Outlet consistency 97.2%    The Water Retention Value (WRV) and number of fiber twists per    millimeter are provided in Table 1, below.

Example 2

Flash Drying a Never-Dried Southern Softwood Kraft Fiber

A never-dried southern softwood kraft fiber (CR-54, available fromBowater Co. of Coosa Mill, Ala., U.S.A.) was made into a slurry and wasdewatered to 19% consistency. Then the fiber was fed into a lab scale2-inch by 2-inch Flash Dryer with 5 to 10 pounds per hour waterevaporation capacity (available from Barr-Rosin Inc. of Bolsbriand,Quebec, Canada). The operations were conducted as follows:

-   1st stage: Inlet temperature 620 degrees Fahrenheit-    Outlet temperature 350 degrees Fahrenheit-    Outlet consistency 58.2%-   2nd stage: Inlet temperature 460 degrees Fahrenheit-    Outlet temperature 250 degrees Fahrenheit-    Outlet consistency—not available (NA)-   3rd stage: Inlet temperature 460 degrees Fahrenheit-    Outlet temperature 250 degrees Fahrenheit-    Outlet consistency 92%    The Water Retention Value (WRV) and number of fiber twists per    millimeter are provided in Table 1, below.

Example 3

Spray Drying/Flash Drying a Never-Dried Southern Softwood Kraft Fiber

A never-dried southern softwood kraft fiber (CR-54, available fromBowater Co. of Coosa Mill, Ala., U.S.A.) was made into a slurry at 0.2%consistency. The slurry was treated with 0.04% Adogen (cationicsurfactant) and 0.2% aerosol (anionic surfactant) sequentially. Thesurfactant treated fiber was fed to a spray dryer with 120 to 155 poundsper hour water evaporation capacity (available from Barr-Rosin Inc. ofBolsbriand, Quebec, Canada). The operations were conducted as follows:

Inlet temperature of 440 degrees Fahrenheit and outlet temperature of191 degrees Fahrenheit. A wheel atomizer was operated at 17.8 K rpm withan air flow rate of 1650 ACFM. The outlet consistency was about 23%. Thespray dryer partially dried fiber was fed into the flash dryer asdescribed in Example 1 and its operation conditions were as follows:

-   1st stage: Inlet temperature 562 degrees Fahrenheit-    Outlet temperature 375 degrees Fahrenheit-    Outlet consistency 63%-   2nd stage: Inlet temperature 431 degrees Fahrenheit-    Outlet temperature 371 degrees Fahrenheit-    Outlet consistency 95%    The Water Retention Value (WRV) and number of fiber twists per    millimeter are provided in Table 1, below.

Example 4

Spray Drying/Flash Drying a Never-Dried Northern Softwood Kraft Fiber

A never-dried northern softwood kraft fiber (LL-19, available fromKimberly-Clark Corp.'s Terrace Bay Mill in Ontario, Canada) was madeinto a slurry at 0.2% consistency. The slurry was treated with 0.2%aerosol (anionic surfactant). The surfactant treated fiber was fed to aspray dryer with 120 to 155 pounds per hour water evaporation capacity(available from Barr-Rosin Inc. of Bolsbriand, Quebec, Canada). Theoperations were conducted as follows:

Inlet temperature of 440 degrees Fahrenheit and outlet temperature of191 degrees Fahrenheit. A wheel atomizer was operated at 17.8 K rpm withan air flow rate of 1650 ACFM. The outlet consistency was about 20%. Thespray dryer partially dried fiber was fed into the flash dryer asdescribed in Example 1 and its operation conditions were as follows:

-   1st stage: Inlet temperature 554 degrees Fahrenheit-    Outlet temperature 417 degrees Fahrenheit-    Outlet consistency 68.5%-   2nd stage: Inlet temperature 473 degrees Fahrenheit-    Outlet temperature 381 degrees Fahrenheit-   Outlet consistency 96%    The Water Retention Value (WRV) and number of fiber twists per    millimeter are provided in Table 1, below.

Example 5

Spray Drying/Flash Drying a Northern Softwood Kraft Fiber and ThenRe-Wetting the Fiber

This example demonstrates the wetness stability of twists of the fibersfrom Example 4. In this example, the fibers were prepared the same wayas in Example 4, except that the fibers were rewet. The rewet fiberswere then dried at 105 degrees Celsius prior to testing their WRV andnumber of fiber twists. These test results are provided in Table 1,below. These test results demonstrate the stability of the twists afterbeing re-wet.

Example 6

Chemical Cross-Linked and Flash Dried Fiber

In this example, chemical cross-linked and flash dried fibers wereobtained from a PAMPERS diaper, manufactured by Procter & Gamble ofCincinnati, Ohio, U.S.A. The WRV and number of twists were determinedand are provided in Table 1, below. TABLE 1 Water Retention Value andFiber Twist Data WRV Yield (gram water/ Number of Twists (percentage offibers with Example gram dry fiber) per Millimeter at least one twist) 10.88 2.78 NA 2 1.28 4.37 NA 3 1.11 2.44 86.2 4 1.22 2.39 96.1 5 1.151.96 89.3 6 0.45 3.24 98Twist Count Image Analysis Method

Dry fibers are placed on a slide and then covered with a cover slip. Animage analyzer (Quankimet 970) comprising a computer-controlledmicroscope (Olympus BH2), and a video camera are used to determine twistcount per millimeter fiber length.

The fiber length of a fiber within a screen field is measured by theimage analyzer. The twist nodes of the same fiber are identified andcounted by an operator using the microscope at 100×. This procedure iscontinued by selecting a fiber randomly, one fiber at a time, measuringfiber length and counting twist nodes of each of the fibers until 100fibers randomly selected with at least one twist node are analyzed. Thenumber of fibers without any twist nodes is also recorded. The number oftwist nodes per millimeter is calculated from the data by dividing thetotal number of twist nodes (N) counted by the total fiber length (L)and/or can be expressed by the following equation:Number of twist nodes per millimeter=N/LThe yield of the twist fibers is determined as follows:% Yield=100^(*)(1−(Tn/(Tn+100)))where Tn is the number of fibers without any twist nodes.

It will be appreciated that details of the foregoing embodiments, givenfor purposes of illustration, are not to be construed as limiting thescope of this invention. Although only a few exemplary embodiments ofthis invention have been described in detail above, those skilled in theart will readily appreciate that many modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of this invention. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention, which is defined in the following claims and all equivalentsthereto. Further, it is recognized that many embodiments may beconceived that do not achieve all of the advantages of some embodiments,particularly of the preferred embodiments, yet the absence of aparticular advantage shall not be construed to necessarily mean thatsuch an embodiment is outside the scope of the present invention.

1. A method of modifying a two-dimensional, flat fiber morphology of anever-been-dried wood pulp into a three-dimensional twisted fibermorphology, comprising the steps of: treating a wood pulp fiber slurrywith a drying aid; and thermally drying the wood pulp fiber slurry at atemperature of at least 200 degrees Celsius.
 2. The method of claim 1,wherein the wood pulp fiber slurry is thermally dried at a temperatureof at least 250 degrees Celsius.
 3. The method of claim 1, wherein thewood pulp fiber slurry is thermally dried at a temperature of at least300 degrees Celsius.
 4. The method of claim 1, wherein the wood pulpfiber slurry is subjected to thermal drying for between about 0.1 andabout 20 seconds.
 5. The method of claim 1, wherein the drying aidcomprises a surfactant.
 6. The method of claim 5, wherein the surfactantis selected from the group consisting of an anionic surfactant, acationic surfactant, and a combination of an anionic surfactant, acationic surfactant, and a non-ionic surfactant.
 7. The method of claim1, further comprising the step of subjecting the wood pulp fiber slurryto a refining treatment prior to treating the wood pulp fiber slurrywith the drying aid.
 8. The method of claim 1, wherein the thermaldrying step is carried out using a flash dryer.
 9. The method of claim8, further comprising the step of fluffing the wood pulp fiber slurryprior to flash drying the wood pulp fiber slurry.
 10. The method ofclaim 8, further comprising the step of removing water from the woodpulp fiber slurry, up to about 30% to about 50% consistency by weight,prior to flash drying the wood pulp fiber slurry.
 11. The method ofclaim 1, wherein the thermally dried wood pulp fiber slurry comprises atleast 80% twisted fibers.
 12. The method of claim 1, wherein thethermally dried wood pulp fiber slurry comprises at least 85% twistedfibers.
 13. The method of claim 1, wherein the thermally dried wood pulpfiber slurry comprises at least 90% twisted fibers.
 14. The method ofclaim 1, wherein a water retention value of the wood pulp is at least0.8 gram water/gram dry fiber as a result of being modified fromtwo-dimensional to three-dimensional.
 15. The method of claim 1, whereina water retention value of the wood pulp is at least 1.0 gram water/gramdry fiber as a result of being modified from two-dimensional tothree-dimensional.
 16. The method of claim 1, wherein a water retentionvalue of the wood pulp is at least 1.1 grams water/gram dry fiber as aresult of being modified from two-dimensional to three-dimensional. 17.The method of claim 1, wherein an average dry fiber twist count of thewood pulp is at least about 2.0 twist nodes per millimeter as a resultof being modified from two-dimensional to three-dimensional.
 18. Themethod of claim 1, wherein an average wet fiber twist count of the woodpulp is at least about 1.5 twist nodes per millimeter as a result ofbeing modified from two-dimensional to three-dimensional.
 19. Acellulosic, fibrous material comprising fibers modified according to themethod of claim
 1. 20. A method of modifying a two-dimensional, flatfiber morphology of a never-been-dried wood pulp into athree-dimensional twisted fiber morphology, comprising the steps of:spray drying a wood pulp fiber slurry; and flash drying the spray driedwood pulp fiber slurry.
 21. The method of claim 20, wherein the flashdrying step includes thermally drying the wood pulp fiber slurry at atemperature of at least 180 degrees Celsius.
 22. The method of claim 20,wherein the flash drying step includes thermally drying the wood pulpfiber slurry at a temperature of at least 200 degrees Celsius.
 23. Themethod of claim 20, wherein the flash drying step includes thermallydrying the wood pulp fiber slurry at a temperature of at least 220degrees Celsius.
 24. The method of claim 20, wherein the wood pulp fiberslurry has a consistency of between about 0.1% and about 10% prior tospray drying the wood pulp fiber slurry.
 25. The method of claim 20,wherein the spray drying is carried out until the wood pulp fiber slurryreaches a consistency of between about 15% and about 50% consistency byweight.
 26. The method of claim 20, further comprising the step ofsubjecting the wood pulp fiber slurry to a refining treatment prior tospray drying the wood pulp fiber slurry.
 27. The method of claim 20,wherein the flash dried wood pulp fiber slurry comprises at least 80%twisted fibers.
 28. The method of claim 20, wherein the flash dried woodpulp fiber slurry comprises at least 85% twisted fibers.
 29. The methodof claim 20, wherein the flash dried wood pulp fiber slurry comprises atleast 90% twisted fibers.
 30. The method of claim 20, wherein a waterretention value of the wood pulp is at least 0.8 gram water/gram dryfiber as a result of being modified from two-dimensional tothree-dimensional.
 31. The method of claim 20, wherein a water retentionvalue of the wood pulp is at least 1.0 gram water/gram dry fiber as aresult of being modified from two-dimensional to three-dimensional. 32.The method of claim 20, wherein a water retention value of the wood pulpis at least 1.1 grams water/gram dry fiber as a result of being modifiedfrom two-dimensional to three-dimensional.
 33. The method of claim 20,wherein an average dry fiber twist count of the wood pulp is at leastabout 2.0 twist nodes per millimeter as a result of being modified fromtwo-dimensional to three-dimensional.
 34. The method of claim 20,wherein an average wet fiber twist count of the wood pulp is at leastabout 1.5 twist nodes per millimeter as a result of being modified fromtwo-dimensional to three-dimensional.
 35. A cellulosic, fibrous materialcomprising fibers modified according to the method of claim
 20. 36. Amethod of modifying a two-dimensional, flat fiber morphology of a slurryof a hydrophilic material into a three-dimensional twisted fibermorphology, comprising the steps of: spray drying a slurry of ahydrophilic material; and flash drying the spray dried slurry of thehydrophilic material.
 37. The method of claim 36, wherein thehydrophilic material is selected from the group consisting ofmicrocrystalline cellulose, microfibrillated cellulose, wood pulp fiber,and combinations thereof.
 38. The method of claim 36, wherein the flashdrying step includes thermally drying the slurry of the hydrophilicmaterial at a temperature of at least 200 degrees Celsius.
 39. Themethod of claim 36, wherein the flash drying step includes thermallydrying the slurry of the hydrophilic material at a temperature of atleast 250 degrees Celsius.
 40. The method of claim 36, wherein the flashdrying step includes thermally drying the slurry of the hydrophilicmaterial at a temperature of at least 300 degrees Celsius.
 41. Themethod of claim 36, wherein the slurry of the hydrophilic material issubjected to flash drying for between about 0.1 and about 20 seconds.42. The method of claim 36, wherein the slurry of hydrophilic materialhas a consistency of between about 0.1% and about 10% prior to spraydrying the slurry of hydrophilic material.
 43. The method of claim 36,wherein the spray drying is carried out until the slurry of thehydrophilic material reaches a consistency of between about 15% andabout 80% consistency by weight.
 44. The method of claim 36, furthercomprising the step of subjecting the slurry of the hydrophilic materialto a refining treatment prior to spray drying the slurry of thehydrophilic material.
 45. The method of claim 36, wherein the flashdried slurry of the hydrophilic material comprises at least 80% twistedfibers.
 46. The method of claim 36, wherein the flash dried slurry ofthe hydrophilic material comprises at least 85% twisted fibers.
 47. Themethod of claim 36, wherein the flash dried slurry of the hydrophilicmaterial comprises at least 90% twisted fibers.
 48. The method of claim36, wherein a water retention value of the hydrophilic material is atleast 0.8 gram water/gram dry fiber as a result of being modified fromtwo-dimensional to three-dimensional.
 49. The method of claim 36,wherein a water retention value of the hydrophilic material is at least1.0 gram water/gram dry fiber as a result of being modified fromtwo-dimensional to three-dimensional.
 50. The method of claim 36,wherein a water retention value of the hydrophilic material is at least1.1 grams water/gram dry fiber as a result of being modified fromtwo-dimensional to three-dimensional.
 51. The method of claim 36,wherein an average dry fiber twist count of the hydrophilic material isat least about 2.0 twist nodes per millimeter as a result of beingmodified from two-dimensional to three-dimensional.
 52. The method ofclaim 36, wherein an average wet fiber twist count of the hydrophilicmaterial is at least about 1.5 twist nodes per millimeter as a result ofbeing modified from two-dimensional to three-dimensional.
 53. Acellulosic, fibrous material comprising hydrophilic material modifiedaccording to the method of claim 36.